Emperor Kangxi (1654-1722) became the second ruler of the Manchu Qing Dynasty. He came to power after his father who was the first emperor of the dynasty died. Kangxi was his imperial name. When he was young, he was called Xuanye. He became ruler when he was eight years old in 1661. He reigned for 61 years, so he was one of the longest-reigning emperors in dynastic history. His grandson Qianlong also reigned for 61 years. He is thought of as one of the greatest emperors because his reign was long, under his rule the Qing Empire started to prosper, dynastic succession was stabilized, and he was comparatively benevolent. Unlike other famous rulers, he didn't kill a lot of people or torture them. Also, instead of heavily taxing the peasants, in the last years of his life he didn't tax them some years because there was enough money in the treasury. Many regarded him as an emperor who loved his people. He was also highly educated and was known as a hard-working emperor who ruled diligently. He learned mathematics, geography and science from the Jesuits, and some of them became trusted advisers and officials. He stands out as one of the best emperors.

Like Kublai Khan at the beginning of the Yuan Dynasty, and Zhu Yuanzhang in the beginning of the Ming Dynasty, during his long rule, he set the policy direction for the empire and stabilized it. He had a somewhat stable court, though one of his own sons tried to usurp power. His main policy decisions were for territorial expansion, continuing the Neo-Confucian bureaucratic system, and trading with and learning from Europeans while resisting their expansion. Under the Ming Dynasty, the Ming Empire developed a somewhat laissez-faire attitude to internal trade and industry. But under the Kangxi Emperor and his successors, the court more carefully controlled commerce and industry and monopolized important industries, reverting to the style of earlier dynastic eras. He also let in a number of Jesuits and appointed them to positions in his court. He valued them for their knowledge and used them as advisers. They helped him in his diplomatic and military affairs, and they helped him modernize the empire. They taught his technicians how to make better guns, cannons and telescopes that the army put to use.

The Kangxi Emperor was eight years old when he became an emperor, but regents ruled the empire in his place. When he was 15, he had a regent named Oboi imprisoned. It was said that Oboi became dangerously powerful to him and that Oboi killed many officials. In this way, he started ruling himself when he was 15.

He was known as a very hardworking emperor. It is said that he worked long hours to read messages and reports and to write out his directives. He had a secret message system involving locked boxes that he used to send messages directly to people. He did this to bypass court officials who he knew were not trustworthy and might try to manipulate things for themselves or usurp power. He spent many hours a day personally directing imperial matters, and he personally went to war in against the Dzungers and was known as a good general. He is also known for being highly educated, literate, and learning a lot from Jesuit advisers in his court. It is said that he learned about world geography, geometry and the Copernican solar system from them. It had a close friendship with some of them. It is said that he wanted European technology introduced in his empire and that Ferdinand Verbiest taught almost every day in the Forbidden City where the rulers and high court officials lived.

In the early and middle years of his rule, he faced some major crises. Wu Sangui (1612–1678) who earlier had helped the Qing dynasty conquer the empire rebelled in 1673. After Wu Sangui helped the Qing army conquer Beijing, he was given the southern regions of Guizhou and Yunnan as a fiefdom. Two other generals were also given big fiefdoms in the south. In 1673, Wu Sangui rebelled together with the rulers of the other two fiefdoms and took control of the south. Qing armies defeated this rebellion. Taiwan was ruled by other rivals who wanted to conquer the empire. Taiwan was also conquered by Qing forces in 1683. The Russians invaded the northern frontier in the 1680s. After a series of battles and negotiations, the two empires signed the Treaty of Nerchinsk in 1689 that secured the borders. Two Jesuits negotiated the treaty. In 1696, he led a Qing army to victory against the Dzungars in the northwest.

These rebellions, wars, and other conflicts killed a large number of people and damaged the economy. In their campaign to put the empire under their control, they killed millions of people. They destroyed the cities along the southern coast and drove the people inland to stop an invasion by Koxinga who used Taiwan as his base and wished to drive the Manchus out. But the empire improved by the time Emperor Kangxi died. Near the end of his reign, there was a time of relative peace and the population grew. New food crops such as corn, peanuts and potatoes helped the peasants to have enough to eat. During his reign, the economy improved and the population started to grow. When he died, there was a big surplus in the imperial treasury.

Maybe Kangxi became a Christian. Some of the Jesuits in his court became trusted advisers and friends. However, he didn't become a Catholic. Some Catholic monks lived with him in the Forbidden City, and he gave funds for building a church. In 1692, he issued an edict that legalized Catholic churches and the practice of Christianity. But there were disputes and rivalries between Catholic sects and Catholics of different nations in his court. A major issue was about whether people could be Catholics and follow traditional customs such as ancestor “worship.” Kangxi said he agreed with the predominant Jesuit view that honoring ancestors was fine to do within certain limits. He was angered at the behavior of certain monks in his court that were sent by the Vatican and by a Papal declaration. Then, he barred missions and closed hundreds of churches. However, in his poems, he expressed that he believed that Jesus was the Son of God and trusted in Jesus for his salvation. He wrote:

Everything as seen by the eye is His creation.He who has no beginning and no end, is Three Persons in One.Heaven's gate was closed to the first man's sin and reopens through the Son.Rid of all false religions, we should become real disciples admired by everyone.